3cx Assistant and Iphone SIP phone

I instal a SIP client on my iphone and it works perfectly, I use it on the same LAN (did not try out)
But if I use call assistant and I dial from it I have no audio receive to my iphone, if I use 3CX softphone instead of my iphone no problem

I dont see what can be wrong on the setting of my iphone !
probably the best could be to have a iphone 3CX softphone but in the meantime...